1. Field Of The Invention
The invention relates to a frequency-doubling circuit for doubling the frequency of a fundamental wave, comprising first and second full-wave rectifier circuits to which the fundamental wave is applied in a mutual phase-quadrature relationship and whose output signals are subtracted from each other to obtain the second harmonic of the fundamental wave.
2. Description Of The Related Art
Such a frequency-doubling circuit is disclosed in U.S. Pat. No. 2,440,465.
Because of the phase-quadrature relationship between the input fundamental waves of the two rectifier circuits, the desired second harmonic of the fundamental wave occurs in the output signals of these rectifier circuits with mutually opposite phases and the unwanted d.c. component and the 4K.sup.th (K=1, 2, 3, . . . ) harmonics occur with mutually equal polarities and phases respectively. By forming the difference between the two output signals, the desired second harmonic of the fundamental wave in each of the two output signals are added together, whilst said unwanted d.c. and higher-order distortion components of one output signal are compensated for by the components of the other output signal.
However, amplitude differences between the output signals of the two rectifier circuits reduce both the efficiency and the distortion compensation. Such amplitude differences occur more specifically when the fundamental wave whose frequency is to be doubled may vary over a comparatively large frequency range, for example when the frequency-doubling circuit is used in a radio or television tuning unit.